Liquid responsive system



Sept. 29, 1942. R. A. WITTMANN' LIQUID RESPONSIVE SYSTEM Filed July 18,1938 2 Sheets-Sheet l Sept. 29, 1942.

R. A. WITTMANN 2,296,969 LIQUID RESPONSIVE SYSTEM Filed July 18, 1938 2Sheets-Sheet 2 2 fig. 2.

Patented 'Sept. 29, 1942 LIQUID RESPONSIVE SYSTEM Robert A. Wittmann,Chicago, Ill., assignor to Chicago By-Products Corporation, acorporation of Illinois Application July 18, 1938, Serial No. 219,935

14 Claims.

My invention relates, generally, to systems responsive to the absenceand presence of liquids, and it has particular relation to such systemsin which Curie point metal is the responsiv element.

My invention can be used in conjunction with boilers, autoclaves,pressure and vacuum kettles, evaporators, stills, condensers, coolingand heating coils, and similar devices where a check on the absence orpresence of liquid is required.

Because of its freedom from moving parts ex-v posed to the liquids inwhich it may be disposed for operation, it is a marked improvementoversimilar systems used heretofore. Since it can be made resistant to orprotected from corrosive liquids and vapors it has a wide application inthe chemical and related industries. Also it can be designed to operateunder substantially all temperatures encountered in practice.

Accordingly, one object of my invention is to provide a systemresponsive to the absence and presence of liquids wherein there are nomoving parts exposed to the liquids and hence eliminating frequentsafety inspections.

Another object of my invention is to provide a system responsive to theabsence and presence of liquids which will operate satisfactorily forlong periods under both continuous and intermittent operatingconditions.

Another object of my invention is to provide a system responsive to theabsence and presence of liquid which can be readily installed in new orexisting equipment.

Other objects of my invention will, in part, be obvious and in partappear hereinafter. I

Accordingly, my invention is disclosed in the embodiments shown in theaccompanying drawings, and it comprises the features of construction,combination of parts, and arrangementof elements which will beexemplified in the constructions hereinafter set forth and the scope ofthe application of which will be indicated in the appended claims.

- For a more complete understanding of the nature and scope of myinvention, reference may be had to the following detailed description,taken in conjunction with the accompanying drawings in which:

Figure 1 illustrates diagrammatically one embodiment of my liquidresponsive system applied to a steam jacketed kettle; I

Figure 2 illustrates diagrammatically another embodiment of my liquidresponsive system applied to a boiler;

Figure 3 illustrates diagrammatically another embodiment of my liquidresponsive system applied to a boiler; and

Figure 4 illustrates diagrammatically still another embodiment of myliquid responsive system applied to what may be either a cooling orheating coil.

Referring to Figure l of the drawings, it will be observed that thereference character 5 designates a'kettle the bottom portion of which issurrounded by a steam jacket 6. For example, this might be a kettle inwhich a liquid is evaporated to remove a desired amount of water. Thesteam jacket 6 may be supplied with steam through the pipe Hi from asteam main through a shut-oil valve shown, generally, at l2. Foraccurate control of the steam supply, a needle valve I3 may be providedin the pipe. The shutoiT valve, I2 is provided with an electric motor IIfor closing it. A hand wheel I5 is provided to manually open and closethe valve l2. The manner in which the motor I4 is operated will bedescribed in detail hereinafter.

. With a view to limiting the level to which a liquid in the kettle 5can be evaporated, a liquid level responsive system shown, generally, at20 is provided. The liquid level responsive system 20 comprises apermanent horseshoe magnet II with two pole extension members 22 and 23extending from the poles thereof. If desired, the permanent horseshoemagnet 2| can be replaced by some other shaped permanent magnet or by anelectromagnet. A non-magnetic plate 24 may be inserted into the sidewall of the kettle 5 with the pole extension members 22 and 23 passingtherethrough as shown. Electrically insulated,

liquid and vapor-proofed, heating coils 25 are wrapped around the poleextension members 22 and 23 as shown, and connected in series circuitrelationship with the terminal leads extending through insulatingbushings 28 and 21. A magneticallyoperated switch shown, generally, at,

the-bottom of the glass container 3|, where, inv

a suitably formed depression or the container 3|, there is deposited apool of mercury 35 in which the conductor. 34 is at all times immersed.The inlead 32 is connected to a coil spring conductor 36 which normallyholds the lower contact end 3? in the pool of mercury 35. This coilspring conductor 36 carries a magnetic armature 8B which, when attractedtowards the adjacent wall of thecontainer 35, causes the lower contactend 31 to leave the mercury pool 35 and thereby break electrical contactwith it to open the circuit between the inleads 32 and The magneticcontrol switch 3@ is so positioned that the magnetic armature 38 isopposite the air gap 39 between the ends of the pole extension members22 and 23.

With a view to furnishing a source of electrical energy for operatingthe motor l6 and the heating coils 25, a pair of energized conductorsGil and M are provided. For example, this source may be the ordinary 110volt alternating current source. The terminal ends ofthe heating coils25 may be connected by the conductors (l2 and 38 to the energizedconductors (it and (it. A switch it is provided in the conductor 53 forcontrolling the energization of the heating coils 25 as desired. Theinlead 32 of control switch as can be connected to the energizedconductor 6i! by the conductor 35. Inlead 33 is connected by means ofconductor (it to one terminal of the motor M. The other terminal of themotor M3 is connected to the energized conductor M by the conductor (Hi.It will be seen that the control switch 3b is in series circuitrelationship with the motor i l.

The pole extension members 22 and 23 are of Curie point metal which,when below their Curie point, are ferromagneticand, when above it, arenonmagnetic. Since there is a large variety of Curie point metals withdii'lerent Curie points or transition temperatures, it is possible tomake a selection for diflerent operating conditions as desired. When theheating coils 25 are energized they will heat the pole extension members22 and 23. However, when the pole extension members 22 and 23 aresurroundedby liquid, the heat will betransferred away to such an extentthat they will not rise above their Curie point and become nonmagnetic.If however the'pole extension members 22 and 23 are not surrounded by aliquid medium, but instead a gaseous medium, the heat from the heatingcoils 25'will not be dissipated so rapidly and the pole extensionmembers 22 and 23 will become nonmagnetic.

It will be seen that when the pole extension members 22 and 23 are belowtheir Curie point and therefore ferromagnetic nearly all of the fluxfrom the permanent horseshoe magnet M will flow across the air gap 39between the ends of the pole extension members 22 and 23. The fluxdensity will then be sufilcient to attract the magnetic armature 38against the force of the coil spring conductor 36 and cause the lowercontact end 31 to leavethe mercury pool 35. thereby opening the circuitbetween the inleads 32 and 33. However, when the pole extension members22 and 23 are heated above their Curie point and are thereforenonmagnetic, the flux density in the air gap 39 will decrease to such anextent that the magnetic armature 88 will no longer be attracted to anextent .suflicient to maintain the control switch 30 in the openpositon.

In operation, assume that the kettle is filled close.

jacket 6. Also, the switch 341 is closed to complete the circuit throughthe heating coils 25. The liquid surrounding the heating coils 25 willconduct the heat away at such a rate-that the pole extension members 22and 23 of the Curie point metal will not be heated above their Curiepoint and therefore the control switch 38 will be in the open position.After a time the liquid level in the kettle 5 will gradually fallpartially or wholly below the permanent magnet 2i as illutrated. Whenthis occurs, the pole extension members 22 and 23 will no longer besurrounded by liquid but they will be surrounded by the gases above theliuid. As the heat from the heating coils '25 cannot now be so rapidlydissipated, the pole extension members 22 and 23 will be heated abovetheir Curie point and become nonmagnetic. When this happens the fluxdensity in the air gap 39 will decrease causing the control switch to toUpon closing of the control switch 3d, the circuit to the motor ill willbe completed. The motor i l on energization operates the shut-oft valve52 to the closed position, thereby shutting oi? the steam supply to thesteam jacket 6. The operator may now draw off the concentrated batch andrefill the kettle 5. The foregoing cycle of operation can thenberepeated. The responsive switches herein disclosed may optionally benormally open or normally closed with appropriate closed or opencircuits, respectively, accordingly. It is well known that before aliquid can 'go into vapor, the temperature must first be raised to theboiling point, and then the so called latent heat of vaporization mustbe supplied to it. In the case of water, the latent heat of vaporizationis a very large quantity. In brief, with a high specific heat to beginwith, and with a large latent heat of vaporization required to vaporizethe liquid after it reaches the boiling point, a body of liquid iscapable of receiving a large amount oi heat, and of keeping itstemperature at no higher than the boiling point even though considerableamounts of heat be conducted to it.

y In the present case, thermal contact of the Curie point material withthe liquid keeps said material from increasing its temperature above theboiling point of the liquid, no matter how much heat is supplied to thebody by the electric heaters 25 or 86 or I00, in Figure l or 3 or 4, orthe gas heater 52 in Figure 2. {The Curie point of the magnetic elementis selected to lie above the boiling point of the liquid. Hence thepresent device cannot operate so long as liquid remains in thermalcontact with the body of Curie point material. That means that thepresent device. provides a sensitive and stable means for detectingliquid level, or the presence of liquid in a given position, which ispeculiarly reliable and durable.

If desired, my liquid level responsive system can be disposed entirelywithin the kettle 5 and the magnetic control switch 30 can be replacedby some other type of magnetic switch. When with a definite quantity ofa liquid to be evaporated to a certain degree and that the quantity issuch that when it isevaporated down to the level of the permanent magnet2|, the desired quantity of water willhave been removed. After the batchhas been put into the kettle 5, the shut-oil valve I2 is opened and theneedlevalve i3 is adjusted allowing steam to pass through to the steamheated. In order to take care of. this requirement the pole extensionmembers" and 23 may shown, generally, at 62.

be selected so that they will become nonmagnetic below this maximumallowable temperature so that the heat supply may be shut off eventhough the liquid is not evaporated to the desired extent. Such aninstallation will respond to either of the aforesaid conditions, namely,it will respond to dropping of the liquid level below the selectedminimum height, or the liquid leaving the locus of thermal contactbetween the liquid and. the element; and, second, it will respond if theliquid is heated to a temperature inexcess of a certain fixed value evenif the level of the liquid be above the selected minimum, or be inposition to make the aforesaid thermal contact.

It will be seen that there are many other applications or" my liquidlevel responsive system illustrated in Figure 1. For example, it may beused equally well to operate shut-off valves in steam, hot oil or gasmains. Another important application is its use in maintaining adefinite liquid level. In this case the magnetic control switch can beconnected in series with the motor of an electric pump which suppliesliquidtoa tank. When the liquid surrounds the heating coils 25, the heatwill be dissipated and the magnetic control switch will be opened,thereby shutting off the motor which operates the pump. lli, however,the liquid level should fall below the pole extension members, the heatfrom the heating coils 25 will not be dissipated to the former extentand the magnetic control switch will be closed thereby starting theelectric motor which drives the pump supplying liquid to the tank. Thepump will continue to operate until the liquid again surrounds the poleextension members and the heat of the heating coils 25 is once moredissipated allowing the magnetic control switch to open and to stop theelectric motor. Also, the

permanent magnet 2! may be located in a tank at the lowervwater levelpoint and the magnetic control switch 30 may be connected to an alarm insuch manner that, once the liquid falls below this lower limit, themagnetic control switch 30 will close. thereby causing the alarm tobesounded.

Referring now to Figure 2 of the drawings, another construction of aliquid level responsive system shown, generally, at 56, is applied to aboiler shown, generally, at 5i, for operation therewith. The boiler 51may be heated by a gas burner 52 positioned at the bottom of thecombustionchamber 53. The combustion chamber 53 is formed by the boilertop 54 and the water leg 55.; Gas is supplied to the has burner 52through a supply line 55 containing a solenoid operated valve 5|.Electric current for opening the solenoid valve 51 is supplied theretofrom a pair of nergized conductors 58 through conductors 55 and 60'. Theconductor 60 contains in series circuit relation a thermostat 6i and aswitch The switch 82 consists of a stationary contact 53 and a movablecontact 64.

The liquid level responsive System50 has as its responsive element a barof Curie point metal 65 extending through th water leg 55 into thecombustion chamber 53. The bar 55 is positioned at the lowest safeoperating water level of the boiler 5|. A rod 65 is adapted to move upand down in a hole provided therefor in the outer end of the bar 85.lower end a permanent horseshoe magnet 61. An extension 68 of the rod 66is provided as support means therefor having 'a diameter greater thanthat of the hole through which the rod 68 is suspended. The extension 68is provided with The rod 66 carries from its heat is conductedtherethrough to its outer end under which the magnet 61 is suspended. So

long as the bar 65 is surrounded by water in the leg suflicient heatwill be dissipated therefrom so that the outer end will remain below itsCurie point and thus will be ferromagnetic. When the outer end is belowits Curie point and ferromagnetic the magnet ill will be attratcted toit and the switch 62 will be closed. If now the thermostat Gl is callingfor heat the circuit to the solenoid valve 51 will be completed and thevalve will be opened allowing gas to flow to the burner 52. Now if thewater in the water leg 55 falls below the bar heat will not bedissipated from it sufiiciently and the outer end will rise above itsCurie point and become non-magnetic allowing the magnet hi to drop andthereby opening the switch 62 and shutting oil the solenoid valve til.

Thus it will be impossible for gas to be supplied to the burner 52unless the water in the water leg 55 is at a level above that of the barof Gurie point metal 65. It will be understood that the boiler 52 mightbe heated by oil or coal and the liquid level responsive system 59 couldbe adapted to close the oil supply valve or stop a Stoker if a low waterlevel should occur.

With a view to providing a liquid level responsive system in which theresponsive element is a body of Curie point metal, which is electricallyheated and which will only be heated when heat is being supplied to theinstallation to be protected, I have provided the system illustrated inFigure 3 of the drawings. In this figure a section' of a boiler 15 maybe provided which is supply line 18 containing a solenoid operated valvel7. Electric current may be supplied for operating the solenoid valveill from a pair of energized conductors 18 through conductors 1.9 and80. The conductor has in series circuit relation therewith a thermostat8i and a switch 82. A member 83 of Curie point metal is provided as theresponsive element being disposed partly within and partly outside theboiler 15. One section of the member 83 is heated by an electricresistance coil 84 which may be supplied with electric energy from theenergized conductors i8 and is in series circuit relation with thethermostat 8!. A horizontal section 85 of the member 83 is providedadjacent to and below the switch 82, beneath which a permanent magnet 86carried on a rod 81 is supported. The permanent magnet 86 operates justas the permanent ma net 61, Figure 2, operates. The rod 81 carries amember 85 of insulating material which is adapted to move the movablecontact 89 of the switch 82 to the open position.

In operation gas can be supplied to the burner heating the boiler 15only when the thermostat aaaaaeo its safety protection is desired. Ifwhen the:

thermostat 8I is calling for heatand when the burner is heating theboiler I5, the water level should drop so that the Curie point member 88is no longer surrounded by water, the heat supplied to the Curie pointmember 83 by the heating coil 84 will not be dissipated sufliciently andthe horizontal section 85 thereof will be heated above its Curie pointand will become nonmagnetic. Upon this occurrence the permanent magnet88 will no longer be attracted to the underside of the horizontalsection 88 and it will drop causing the switch 82 to be opened as shownin the drawing. When the switch 82 is opened the circuit to the solenoidvalve 11 will be broken and the gas supply to the gas burner will beshut oil, preventing damage to the boiler I5 due to low water leveltherein. It will thus be seen that a very reliable and economical safetysystem is eiIected.

Failure of the cooling water supply to cooling coils employed in variousinstallations may easily result in serious damage. .Thus in the casewhere large transformers are. kept from overheating by cooling coilstherein the failure of the cooling water supply in such instances maycause the destruction of the transformer. In order to provide againstsuch and similar destruction I have provided a system responsive to thepresence and absence of liquid as shown in Figure 4 of the drawings. Acooling coil shown, generally, at 9.", may be taken as representative.of one that might be used in a transformer, condenser or otherinstallationfln the outlet pipe 98 of the cooling coil 95 a pipe fitting91 is interposed through which a member 98 of Curie point metal extends.

A hole 99 in the member 98 allows cooling water to flow therethrough.The projection of the member 98 extending to the left of the pipefitting 91 is heated by an electric heating coil I88 which is suppliedwith current from a pair of energized conductors I8I. "the heating coilI88 so that the projection of the Sufficient heat is supplied by member98 extending to the right of the pipe fitting 91 is heated above itsCurie pbint and becomes non-magnetic when cooling water is not flowingthrough the pipe fitting 91 and conducting heat away from the member 98.When cooling water is flowing, unless its temperature the energizedconductors IM to an electric operating device I81. In the case where thecooling c il 95 is used .in connection with a transformer this electricoperating device I81 might be adapted to operate a switch permitting thetransformer to be put in or out of service. Thus in operation assumethat the cooling coil 95 is disposed in a transformer and that theproper supply of cooling water is flowing thereto. In this condition theright hand projection of the Curie point member 98 will be cooled belowits Curie point andthe magnet I82 will be attracted'to it closing thecontacts I85 and I 88 and thereby allowing the electric operating deviceI8I to put the transformer in service. Now if the cooling water 75supply shouldfail for some reason the member 98 will become heated aboveits Curie point and become non-magnetic allowing the magnet I82 to dropand thus opening the circuit to the electric operating device I81,thereby causing the transformer to be taken out of service andpreventing damage thereto.

- The Curie point metal may be selected to respond at such a valuethatif the liquid itself becomes too warm, the control circuit will beswitched, without reference to the separate heat input means I88. Or theCurie point metal may be responsive to the combined effect of theelectrical heat input and the temperature of the I cooling or condensingmedium.

The level control herein disclosed may be employed for high level aswell as for low level by causing the liquid at high level to effect anabstraction of heat to produce a response of the switch. A I

In the disclosure herein where the heat of electric current flow isrelied upon the heater may burn out.

The circuit may optionally be arranged to rely upon the current carryingproperties of the heater wire to maintain the system in operation. Thatis to say, the heater wire may serve as a fuse to shut off the current;from the rest of the system. Alternatively, a relay in circuit with theheater may operate upon the current supply or it may control one or morecircuits to take the system outof operation or. perform any other safetyor emergency operation such as shutting down the system or a part ofthe-same. Thus, forexample, it may cut out the burner or the motor orthe like.

It will be understood that wherever permanent horseshoe magnets havebeen used they may he s replaced by electro-magnets and permanentmagnets in other shapes.

Since certain further changes can be made in the foregoing construction,and different embodiments of the invention may be made without de-"parting from the scope thereof, it is intended that all-matter shown inthe accompanying drawings or described hereinbefore shall be interpretedas illustrative and not in a limiting-sense.

I claim as my invention:

1. In a system responsive to the-presence and 59 absence of liquidindependently of the temperature of the liquid, in combination, aresponsive element of Curie point metal, means independent of saidliquid for heating said responsive element above its Curie point torender the-element nonmagnetic, a container for liquid associated withsaid element and adapted to bring liquid into thermal contact therewith,thermal contact of.

liquid in said container with the element serving to dissipate the heatof said heater and to cool the elementbelow its Curie point whereby itbecomes magnetic, a source of flux interacting with said responsiveelement, and means external to the container controlled by interactionof said responsive element and said source of flux.

' 2. In a system responsive to the presence and absence ofliquidindependently of the temperature of'the liquid, in combination, aresponsive element of Curie point metal, means adapted to contain liquidin which the element is adapted to be immersed, means independent of theliquid for-heating said responsive element above its Curie point when itis not suiliciently cooled by being immersed in said-liquid, a sourceof. flux interacting with saidresponsive element as a function of itsmagnetic condition, and means .external to the liquid containing means,said last named means being controlled by the interaction of said sourceof flux and said responsive element.

3, In a liquid level responsive system, in combination, a source offlux, spaced apart extension means including a responsive element ofCurie point metal extending from the opposite magnetic poles of saidsource of flux, means for heating said responsive element above itsCurie liquid container adapted to contain liquid the level of which mayfluctuate above and below a predetermined level, said element beingsubject to thermal contact with the liquid when the level magnetic polesof said source of flux and adapted to be operated when said responsiveelement is not immersed in liquid.

4. In a liquid level responsive system, in com bination, a source offlux, spaced apart responsive elements of Curie point metal extendingfrom the opposite magnetic poles or said source of flux, heatingelements disposed to heat said spaced apart responsive elements to raisethem above the Curie point, whereby the said elements becomesubstantially non-magnetic, a container for liquid, the level oiwhichliquid varies in respect to a predetermined level, said liquid uponattaining said predetermined level coming in thermal contact withsaidelements and cooling the same below the Curie point whereby they becomemagnetic, a circuit means connecting said heating elements and a currentsource, and a magnetic switch disposed adjacent to the ends Curie point.

7, In a liquid level responsive system, in combination, a responsiveelement of Curie point metal, means for heating said responsive element,a magnet adapted to be attracted to said responll) sive element when iLis ferromagnetic, said point to render the element non-magnetic, a

switch means operated by said magnet, said element comprising aplurality of sections, a heating coil for heating one section or saidresponsive element, means for immersing another section thereof inliquid, and another section thereof of the liquid rises to or above saidpredetermined attracting said magnet when ferromagnetic, electriccurrent being supplied to said heating coil only when the liquid levelresponsive system is in operation 8. In a system responsive to thepresence and absence oi fluid flow, in combination, a responsive elementof Curie point metal comprising a plurality of sections, one section ofwhich is positioned in a path of fluid flow, means for continggg uouslyheating another section or said responsive element, magnet meam adaptedto be attracted to another section or said responsive element when saidlast named section is at a temperature below its Curie point due to thepresence of fluid 39 in thermal contact with said first named section,

and switch means operated by said magnet means.

9. A device responsive to the presence of a body of liquid independentlyor the temperature of the liquid, comprising a body of Curie point admaterial the Curie point or which lies above the boiling point oi theliquid, heating means independent of the liquid in thermal conductiverelation to at least a part of said body to heat said body when the bodyis out oi thermal contact Of Said Spaced apart responsive elements 9-Waylit with the liquid to a temperature above the Curie from the oppositemagnetic poles of said source or magnetic flux and adapted to beoperated when said spaced apart responsive elements are not cooled bysaid liquid.

5. In a liquid level responsive system, in combination, a permanenthorseshoe magnet, spaced apart responsive elements of Curie point metalextending from the opposite magnetic poles or 1 said horseshoe magnet, acontainer for liquid, the level or which varies in'respect to avpredetermined level, said liquid upon attaining said predetermined levelcoming in thermal contact with said elements and cooling the same belowthe Curie point whereby they become magnetic, heating coils surroundingsaid responsive elements for heating them above their Curie point whennot cooled by said liquid, circuit means for interconnecting saidheating coils and a current source, and a magnetic switch disposedadjacent responsive element when it is at a temperature below its Curiepoint, and switch means operated by said magnet, one section of saidresponpoint which will render a selected part of the same non-magnetic,and liquid containing means r in winch/a body or liquid may be broughtinto thermal contact with said body to abstract sumcient heat from thebody to bring said selected part below the Curie point and to render thesame magnetic, and control means responsive to the magnetic ornon-magnetic condition of said selected part of the body.

iii; A device sensitive to contact with a liquid comprising heatingmeans, a vessel adapted to contain a liquid, a body of Curie pointmaterial in thermal contact with the heating means and adapted to becontacted with liquid When the 55. same occupies a predeterminedposition in said vessel, the heating means being adapted to raise thetemperature of the Curie point material to the Surie point to render thesame non-magnetic when said material is out of thermal contact with gothe liquid, thermal contact of the liquid dissipating the heat added bysaid heating means to the extent or cooling 9. selected part of the samebelow the Curie point and thereby rendering the same magnetic, andcontrol means including an electric switch responsive to the magnetic ornonmagnetic condition of said selected part of the body.

11. In combination, a permanent magnet, a body ot-Curie point material,means including a 7 0 switch responsive to extension of the field of themagnet through the body of Curie point material when the same isdiamagnetic, heating means for heating the Curie point material when thesame is out of thermal contact with a body sive element being exposed tosaid heating means, of liquid to the Curie point whereupon it becomesparamagnetic, and means adapted to cpntain liquid which when in thermalcontact with the body conducts away heat fast enough to keep the bodybelow the Curie point.

12. Means responsive to :the presence or absence of liquid-in apredetermined space comprising in combination a body of Curie pointmaterial having a Curie point above the boiling point of the liquid,means apted to confine liquid in'thermal contact with a portion of,

said body for-the purpose of limiting the temperature of said portion toa value-below the Curie point or the material, means independent oi. theliquid for continuously adding heat to said body, said means beingcapable in the absence ot-heat removal by said liquid of raising thetemperature'oi said body above the Curie controlled by the interactionof said body and I liquid contact with said body which liquid is adaptedto carry heat away from: said body so long as the liquid is in thermalcontact with the body to keep said. body below the Curie point, a sourceor magnetic flux interacting with said body hr one manner when the bodyis below its Curie point, and in a diflerent manner when the body is ator above the Curie point, and means,

said source of flux.

14. In combination, a vessel in which liquid is,

adapted to be contained above a certain level, a body oi. Curie pointmaterial in thermal contact with liquid above said level, the Curiepoint of said material being above the boiling point of said liquid,heating means in'thermal conductive relation to said body, for supplyingheat to the body at a rate faster than said body can dissipate the minthe absence or thermal contact with; I}

said liquid, a source oi. magnetic flux interacting with said body, andmeans controlled by inter- 7 action of said body and said source offlux,

' ROBERTA.WI'ITMANI V.

